Pressure moulding machines and mould parts therefor

ABSTRACT

In a pressure moulding machine, particularly a die casting machine, detection of locking together of the die parts by the applied pressure is effected by detecting the resulting mechanical stretch in the machine frame; the die parts are opened and closed together by an air motor associated with a hydraulic motor that damps the opening and closing movement of the dies, the die parts being locked together by the hydraulic motor; full closing of the die parts is determined by applying pressurized air to bores therein and to a controlling pressure switch, the pressure switch not being operable if air is leaking from the bores.

FIELD OF THE INVENTION

The present invention is concerned with improvements in or relating topressure moulding machines, especially to die casting machines, and inor relating to mould parts for such machines.

REVIEW OF THE PRIOR ART

Die casting is a widely employed technique using various metals (usuallyof relatively low melting point) and plastic materials, because of thepossibility for inexpensive production of relatively complicated shapesonce a suitable die mould has been provided. A common way of increasingproduction in this field is use of a machine of increased size as to theweight of cast material employed in a single shot, and then to provide amultiple-cavity mould with the maximum number of cavities that can beused.

Such large machines however introduce their own problems in that theyare high pressure machines inherently that are expensive to manufactureand operate. Moreover, because of the large size of the moving parts,involving considerable inertias they are somewhat slow in operation,resulting in fewer "shots" per unit time. The large multi-casting diesare expensive and any damage thereto is consequently more costly. It isalso found that difficulty is experienced in obtaining castings of therequired quality from all of the cavities, usually due to inadequateflow of material through the passages provided in the die for thatpurpose, and the inadequately-fed cavities must be closed off, resultingin decrease in production.

DEFINITION OF THE INVENTION

The approach to achieve high ecomonic production employed with machinesin accordance with the invention is to provide a simple, fast-actingmachine capable of safe, automatic, relatively unattended operation.Such a machine can therefore be employed with dies having only a smallnumber of cavities, usually only one cavity, and yet can achieve aneconomic high production rate because of the speed at which it can begot into satisfactory operation, the relatively high number of shots canbe obtained per unit time, and the possibility that several of suchmachines on automatic operation can be tended by a single operator. Itwill be seen that such a machine provides for high flexibility ofoperation, particularly for a manufacturer involved with relativelyshort production runs.

Nevertheless, the principles embodied in machines in accordance with theinvention are applicable to die casting machines in general, and notonly to the small machine particularly described herein by way ofexample.

It is the principal object of the present invention to provide a newdie-casting machine and new mould parts therefor.

It is a more specific object to provide a new machine especiallysuitable for safe relatively unattended operation.

It is another more specific object to provide a new machine adapted forfast automatic operation.

In accordance with the present invention there is provided incombination with a pressure moulding machine comprising a machine frame,means for mounting the two mould parts by the frame for movementrelative to one another for opening and closing the mould cavity formedby the two mould parts, motor means operatively connected to one mouldpart to move it relative to the other part and to hold the parts withtheir respective mating faces in mating engagement with one anotherunder pressure during a mould filling operation, means for supplying airunder a pressure different from ambient to one of the mould parts andfor detecting movement of air from between the mold part mating facescaused by lack of mating engagement of the said faces; the combinationcomprising one of the mould parts having a bore therein for receivingthe said air, the bore extending to a part of the said mating face ofthe mould part such that its opening to the respective mating face isspaced from the mould cavity.

Preferably the combination comprises another mould part having a boretherein extending to the face thereof which mates with the said matingface of the first-mentioned mould part, the last mentioned boreregistering with the bore in the first-mentioned mould part.

The said bore may extend completely through the mould part from the saidmating face to another face thereof, and the combination comprises asoft metal washer for interposition between the last-mentioned mouldpart face and the machine frame to receive solid particles trappedbetween the last-mentioned mould part face and the machine frame andprevent leakage of air between the bore and the ambient atmosphere dueto the presence of such particles.

DESCRIPTION OF THE DRAWINGS

A die casting machine which is a particular preferred embodiment of theinvention will now be described, by way of example, with reference tothe accompanying drawings wherein:

FIG. 1 is a general perspective view to show the main structure of themachine,

FIG. 2 is a plan view from above with parts broken away as necessary toshow the construction,

FIG. 3 is a schematic of the machine to permit description of the mannerin which the die parts are moved toward each other and locked togetherduring the die casting operation,

FIG. 4 is an exploded view of the "fixed position" die part to show itsconstruction,

FIG. 5 is a view taken on the line 5--5 of FIG. 2, to show thearrangement for mounting the machine pump,

FIG. 6 is a schematic diagram of the electrical circuit of the machine,

FIG. 7 is a schematic diagram of a die temperature control circuit, and

FIG. 8 is a schematic diagram showing two alternative systems fordetecting the closing of the dies for injection of the metal shot.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated above, the moulding machine to be particularly described isa die-casting machine intended for the casting of objects from readilymelted metals, such as zinc, lead, aluminum and their alloys. Theapplication of the invention to machines for moulding and casting fromother materials will be apparent to those skilled in the art.

The machine is mounted on the flat-top 10 of a table 11 to be at aconvenient height for the operator, while the necessary electricaloperating equipment such as relays, switches, indicator lights andmeters etc. are mounted on a suitable console (not shown) alongside thetable. A bath 12 of the liquid metal to be cast is provided at one endof the table, the bath being provided with conventional pre-heatingfacilities for metal ingots which are fed thereto, and with aconventional thermostatic control (not illustrated) to maintain themetal in the bath at the desired liquidus temperature.

The basic machine structure involves four spaced, parallel flat rigidplates 13 through 16 which are rigidly connected to one another. Theplate 16 is fastened to the table top 10 while the other plates arepermitted to slide freely thereover, as will be further described below.The plates 13 and 14 have interposed between them a cylindrical member17 constituting an air or pneumatic cylinder containing a doubleactingpiston 18 mounted on a piston rod 19 carried in suitable bearings in theplates 13 through 15. The plates 14 and 15 have interposed between thema cylindrical member 20 constituting a liquid or hydraulic cylindercontaining a double-acting piston 21 also mounted on the shaft 19. Theplates 15 and 16 are connected together by four relatively massive rods22, which also constitute slide guides mounting a movable die platen 23which is fixed to the end of the piston rod 19 and is moved therebytoward and away from the plate 16, which constitutes the cooperatingfixed die platen.

Air under pressure is supplied from a suitable source to one or otherside of the piston 18 under the control of respective solenoid valves24. This air is also supplied under the control of a valve 25 to anair-operated hydraulic booster motor 26 mounted to one side of the plate14 and having a double-acting piston 27 mounted on a piston rod 28 thatcan protrude into a special passageway section 29 provided in the plate14. With the piston 27 in the retracted position shown in FIG. 3 theliquid in the hydraulic circuit can pass relatively freely from one sideof the piston 21 to the other via a connecting pipe 30, a pressurisedreservoir 31 being provided to maintain the circuit full of liquid.

The movable platen 23 is water-cooled and a water-cooled movable orejector die mould part 32 is mounted on two transversely-spaced spacerplates 33 which are in turn mounted on the platen 23. The ejectormechanism illustrated herein comprises a plate 34 mounted on two pins 35which slide freely in the platen 23 and force the plate 34 against theback of the ejector die 32 as the dies open by the engagement of thepins with plate 15; the ejector pins in the die (not shown) are forcedforward by the plate 34 to eject the cast workpiece. Any other ejectormeans common in the art can of course be used in place of thoseparticularly described, such as a separate piston rod coaxial with therod 19 and operated at a specific time in the machine operation.

Referring now especially to FIG. 4, the fixed or cover die mould die 36of the invention differs from that known hitherto in that it is mountedto the fixed platen 16 by means which locate it accurately transverselyof the platen, but which permit it to move longitudinally as the diesare opened and closed. In the embodiment particularly illustrated thedie 36 is mounted for such movement on two parallel rods 37 extendingfrom the platen 16 and is retained thereon by a pin 38 which enters alongitudinally elongated slot 39 in one of the rods 37. The die carriestwo compression springs 40 which engage a soft metal washer 41 (whosefunction will be described below) and urge the die away from the platen.

A concave recess 42 in the rear face of the die receives the nozzle 43of the metal pump 44 to be described below. The pump also is mounted tobe movable longitudinally of the machine and for this purpose a frame 45mounting the pump is slidably mounted on extensions of the rods 22 bymeans of bearings such as 45a. The ends of the two lower rods 22 arescrew-threaded and are provided with adjusting nuts 46 engagingrespective spring belleville washers 47. The pump housing 48 slides onguides 49 and is held against longitudinal movement by a bar 50 engagedby the washers 47 and engaging the housing via a central vertical pivotbar 51. The pump housing extends downwards into the metal bath and isheld against vertical movement by clamp bars 52 reacting against theupper bearings 45a and held by adjusting screws 53.

The pump is actuated when required by an air-operated motor 54controlled by a solenoid valve 55, the plunger 56 of the motor beingseparably connected to the piston 57 of the pump. The part of the pumpnozzle between the housing and the back of the platen 16 is surroundedby a shroud 58 into which a gas torch discharges to pre-heat the nozzleand to prevent the metal freezing therein.

Referring especially to FIG. 2 a lever 59 has one end pivoted at 60 tothe table top 10, while the other end engages the control member of asensitive micro-switch 61. a longitudinally-adjustable contact screw 62mounted on the lever close to the pivot 60 engages the end plate 13. Itwill be seen that the lever detects and amplifies any longitudinalmovement of the end plate 13, which slides freely on the table, andactuates the switch 61 when this movement is a predetermined amount.Another air-operated motor 63 controls the movement of a head 64 tospray the dies with a small quantity of a lubricant after each mouldingoperation.

Some of the pressurised air that is fed to the air motor 17 is bledtherefrom via a regulator 65 and fed via a variable orifice 66 to apassage 67 in the movable die, this passage discharging from the dieface that mates with the corresponding face of the fixed die via anorifice 68 that is spaced from the respective part of the mould cavity.A passageway 69 in the fixed die has an orifice 70 also spaced from therespective part of the mould cavity and registering with the orifice 68,this passage passing completely through the die. A variable timingorifice 71 is connected between the orifice 66 and passage 67 and isconnected via a timing reservoir 72, which in this embodiment consistsmerely of the length of pipe 72, to a pressure sensitive switch 73. Avent groove 74 is provided around the orifice 70 to ensure that any airescaping therefrom cannot reach the die cavity while the dies are closedand it is full of molten metal. A check valve 93 allows the reservoir toempty quickly when pressurised air is no longer fed thereto. The diesare supplied with water for cooling purposes via a solenoid-controlledvalve 75 while the temperature of the water discharged therefrom isdetected by a sensor 76.

In operation of the device the pump is placed in position, the pump bodysliding easily into place since its operative dimensions are calculatedto be exact when it is at the operating temperature. The pump is nowheated by its contact with the hot metal in the bath and by the torchuntil it is at the desired operating temperature. The dies are mountedin position and the air and water hoses connected thereto.

Pressurised air (e.g. at about 80-100 p.s.i.) is now supplied to the airmotor 17 which moves the piston 18 forward (to the right as seen in thefigures) to close the dies together. This forward movement is dampenedin a desired manner by the movement of the piston 21 in its cylindersince this must be accompanied by flow of liquid from one side to theother. With the piston 18 in its fully forward position the boostermotor 26 is now operated by admitting air thereto. The first movement ofthe piston closes the by-pass passage against movement of liquidtherein, and subsequent movement increases the pressure in the hydrauliccylinder to the value required for complete closing of the die while themoulding operation takes place (e.g. about 2000 p.s.i.)

One effect of the application of these high pressures is to stretch thewhole machine, especially between the plates 14 and 16 which aresubjected to the hydraulic pressure, and the end plate 13 slides acorresponding small amount (e.g. about 0.005 inch) on the table top 10.The movement detector constituted by the lever is now adjusted until theswitch is just positively operated by a movement of this extent. It willbe seen that detection by this means is extremely positive, in that itis only effective if the required pressure is applied, and then only ifthis pressure is applied via the closed dies, since otherwise the bodyof the machine cannot stretch. This may be contrasted with anarrangement for example in which the hydraulic pressure is measured; themaximum pressure will be obtained and indicated even in cases where thedies may be jammed open.

Although in this specific embodiment a mechanical movement detector hasbeen described, comprising a lever system providing amplification of thedimensional change of the machine frame, other detectors can beemployed, such as optical or electrical devices used for measuring andindicating small mechanical displacements.

The pump is now moved longitudinally by operation of the adjusting nuts46 until the pump nozzle 43 is pressed sufficiently firmly into the rearrecess 42 in the die for the liquid metal to be fed to the die withoutsubstantial leakage. The machine is now essentially ready for operation,subject to various minor adjustments that will be described below.

As described above, the machine is now operated by supplying air to themotor 17, whereupon the dies close together. If the dies do not closefully, or if the movable die 36 is not pressed firmly home against thewasher 41 and the fixed platen 16, then air escapes and the pressureapplied to the switch 73 is insufficient to operate it and the machinecannot continue its operation until the attendant has checked the reasonfor the failure. The function of the soft washer 41 is to preventmalfunction in the event that a minor foreign body, such as a smallpiece of dirt, becomes interposed between the die part 36 and the fixedplaten 16; such a body instead becomes embedded in the washer under thepressure applied thereto.

With the dies fully closed the switch 73 is operated after a period oftime determined by the parameters of the variable orifices 66 and 71 andof the reservoir 72. The booster motor 26 can now be operated andincreases the clamping pressure between the die parts to the elevatedvalue necessary for the casting operation. The switch 61 detects whetheror not the required pressure has been applied by the booster motor and,if so, permits operation of the pump motor to force a "shot" of liquidmetal into the die. After a predetermined period required forsolidification of the cast workpiece the operation of the booster motor26 is reversed releasing the pressure, and thereafter the operation ofthe motor 17 is reversed to open the die parts, the workpiece beingejected as the ejection pins 35 become operative. While the die partsare opened the motor 62 is operative and moves the spray head 64 tospray the cavity faces with a release agent. The cycle then repeats.

Referring now to the schematic circuit diagram of FIG. 6 power issupplied from a conventional source via main switch 74 to two busbarsbetween which the various switches and relays etc., are connected, theconventional indicator light 77 being provided.

To open and close the dies under control of the operator, as describedabove for adjustment of the switches, etc., push button 1PB is closedand energises relay 1CR. If the dies are open and retracted then aswitch 78 (ILS) adjustably mounted on the plate 33 and operated by theretracted movable die is open and relay 5CR is not operated; the switch73 (IPS) will also be open and relay 8CR not operative; the switch 61(2LS) also is open and the relay 6Cr inoperative; with closure of 1PBthe dies are moved together by air motor 17 under control of therespective relay valve 24 (1 SOL). The normally open contacts 1CR inseries with normally closed contacts 2PB keep relay 1CR and solenoid1SOL energised. Pressing 2PB opens its contacts and energises 1CR and1SOL to open the dies.

To run with operator controlled single cycles the dies are closed by 1PBand 4PB is then pressed momentarily to energise 10CR which is then heldenergised by associated 5CR and 10CR contacts. If 1CR and 8CR areenergised then 2CR will energise to energise 2SOL for operation of valve25 and consequent operation of the booster motor, locking the diesclosed. 2LS is now actuated by the stretch of the machine and 3Cr isenergised, energising 3SOL to operate valve 55 and drive down theplunger of the metal pump. As the pump plunger begins to descend 3LS isactuated to energise relay 7CR, which is then locked energised and inturn applies power to a shot timer relay 11CR and a die timer relay12CR. When the shot timer relay 11CR times out and energises itde-energises 2CR, 2SOL, 3CR and 3SOL to unlock the dies and returns thepump piston to its upper position, stopping the feeding of metal to thedies. When the die closed timer relay 12CR times out it deenergises 1CRand 1SOL to open the dies. When the dies are open 1LS energises 5CRwhich terminates the single cycle by deenergising 10CR; power is thenremoved from 11CR and 12CR by de-energisation of 7CR.

For automatic operation the dies are closed and 4PB is pressed asbefore. When 6CR is energised and the machine locked then 3PB is pressedmomentarily to energise 9CR which is then locked in, the relay 9CRreplacing the single cycle relay 10CR. The cycle proceeds as beforeuntil the dies are open and the moulded part has been ejected. Power isnow applied to the part sensing amplifier 80 which senses the part byits operation of switch 81 and energises 4CR, which in turn energises1CR and 1SOL to close the dies and start the next cycle. The timing ofthe auto-timer relay 13CR is stopped when 3CR is energised andre-started when it de-energises; the machine continues to cycle untilpower is removed or if re-cycling does not occur within an alloted timeand 13CR times out.

The die closed detector constituted by the die orifices, associated airsupply and switch 73 also functions as a temperature detector for thedie to ensure that it does not become overheated or overcooled. Thus ifthe die becomes locally overheated its mating faces in contact with thehot metal expand and bend to a convex shape, permitting air to escapeand increasing the period required to operate the switch 73(1PB). Ifthis effect becomes too great then the timing relay 13CR will time outbefore 1PB is operated stopping the machine completely. A similar effectis obtained if the die runs too cool because of excessive water to therear of the die, so that the die will be maintained at the hightemperature preferred for free flow of the metal to give good castingquality and long die life.

It is also found that apparatus in accordance with the inventionprovides during operation an inherent self-regulation of the temperatureof the pump nozzle 43. For example, if the nozzle becomes too hot itwill expand in length beyond the optimum setting and increase itscontact pressure with the die recess 42, thereby increasing the heattransfer between them. In addition there is an increase in the timeinterval between the instant when the dies are closed by the motor 17,and those when the dies are locked by motor 26 and a shot of metal ispumped to the die, since the pump must be moved backwards a greaterdistance against the spring 47 and more pressure must therefore beapplied; this increasing time interval again increases the temperatureloss to the die. The effects are reversed if the nozzle is too cool,giving the nozzle greater opportunity to heat to the optimumtemperature.

FIG. 7 shows an addition to the electrical circuit to give automaticcontrol of the die temperature, as described above, by modulation of theperiod for which water flows in the dies. Thus, the detector 76illustrated in FIG. 1 is a diode, thermistor or other temperaturesensitive impedance connected in shunt with a capacitor 82. Thecapacitor is supplied with charging current via switch contacts CR14, avoltage controlling zener diode 83, an ambient temperature compensatingdiode 84 and a time-setting variable resistor 85. As the temperature ofdetector 76 increases its impedance decreases, increasing its shuntingof the capacitor 82 and increasing the time required before aunijunction transistor 86 is energised, in turn energising an SCR device87 and the relay CR14 which controls water valve 75. As the temperatureincreases therefore the period for which the valve 75 is open increasesto increase the quantity of water supplied thereby to the dies.

FIG. 8 illustrates an alternative system for sensing the closing of thedies in addition to the back pressure system already described above. Inthis alternative system a regulator 90 feeds through a variable orifice91 to the fixed die 23 and thence through orifices 68 and 70 to a bore69 in the movable die 36. The bore 69 feeds the air thus received to atiming orifice 92 and a check valve 93 to the reservoir 94 and valve 73.The check valve 93 allows the reservoir to drain quickly when the diesopen so that it is again ready to perform its timing function.

I claim:
 1. In combination with a pressure moulding machine comprising amachine frame, means for mounting two mould parts by the frame formovement relative to one another for opening and closing the mouldcavity formed by the two mould parts, motor means operatively connectedto one mould part to move it relative to the other part and to hold theparts with their respective mating faces in mating engagement with oneanother under pressure during a mould filling operation, means forsupplying air under a pressure different from ambient to one of themould parts and for detecting movement of air from between the mouldpart mating faces caused by lack of mating engagement of the said faces;the combination comprising one of the mould parts having a bore thereinfor receiving the said air, the bore extending to a part of the saidmating face of the mould part such that is opening to the respectivemating face is spaced from the mould cavity.
 2. A combination as claimedin claim 1, and comprising another mould part having a bore thereinextending to the face thereof which mates with the said mating face ofthe first-mentioned mould part, the last mentioned bore registering withthe bore in the first-mentioned mould part.
 3. A combination as claimedin claim 1, wherein the bore extends completely through the mould partfrom the said mating face to another face thereof and comprising a softmetal washer for interposition between the last-mentioned mould partface and the machine frame to receive solid particles trapped betweenthe last-mentioned mould part face and the machine frame and preventleakage of air between the bore and the ambient atmosphere due to thepresence of such particles.
 4. A combination as claimed in claim 1,wherein the said mating face of the said mould part having a boretherein is provided with a groove surrounding the opening of the bore tothe mating face and open to atmosphere to receive and discharge toatmosphere air escaping from the said bore opening.
 5. A combination asclaimed in claim 1, wherein one mould part is mounted in the machineframe for movement in the direction of movement of the mould parts toopen and close the mould and the last-mentioned part comprises boreholes therein with longitudinal axes parallel to the said direction ofmovement of the mould parts for receiving mounting pins of the machineframe on which the mould part is mounted for said movement thereof. 6.In combination with a pressure moulding machine comprising a machineframe, means for mounting two mould parts by the frame for movementrelative to one another for opening and closing the mould cavity formedby the two mould parts, motor means operatively connected to one mouldpart to move it relative to the other part and to hold the parts withtheir respective mating faces in mating engagement with one anotherunder pressure during a mould filling operation, means for supplying airpressure higher than ambient to one of the mould parts and for detectingescape of air from between the mould part mating faces caused by lack ofmating engagement of the said faces; the combination comprising one ofthe mould parts having a bore therein for receiving the said air, thebore extending to a part of the said mating face of the mould part suchthat its opening to the respective mating face is spaced from the mouldcavity.
 7. A combination as claimed in claim 2, wherein the said anothermould part is mounted in the machine frame for movement in the directionof movement of the mould parts to open and close the mould and thelast-mentioned mould part comprises bore holes therein with longitudinalaxes parallel to the said direction of movement of the mould parts forreceiving mounting pins of the machine frame on which the mould part ismounted for said movement thereof.
 8. A combination as claimed in claim3, wherein the said last-mentioned mould part is mounted in the machineframe for movement in the direction of movement of the mould parts toopen and close the mould and the last-mentioned mould part comprisesbore holes therein with longitudinal axes parallel to the said directionof movement of the mould parts for receiving mounting pins of the macineframe on which the mould part is mounted for said movement thereof.
 9. Acombination as claimed in claim 6, wherein one mould part is mounted inthe machine frame for movement in the direction of movement of the mouldparts to open and close the mould and the last-mentioned mould partcomprises bore holes therein with longitudinal axes parallel to the saiddirection of movement of the mould parts for receiving mounting pins ofthe machine frame on which the mould part is mounted for said movementthereof.
 10. A combination as claimed in claim 9, wherein the said onemould part has the bore therein extending from its mating face to theopposite face thereof and comprising a soft metal washer forinterposition between the said opposite mould face and the machine frameto receive solid particles trapped between the last-mentioned mould partface and the machine frame and prevent leakage of air between the boreand the ambient atmosphere due to the presence of such particles.